How to integrate Jsoup in GWT

I am trying to develop a simple app with Jsoup. For that, I have replaced the default code in the StockWatcher.java file from GWT with my code, which requires Jsoup. I have downloaded the Jsoup jar file from http://jsoup.org/download (the first link), and placed it in the StockWatcher/war/WEB-INF/lib folder. After this, the Jsoup classes are imported into the class all right (there is no red colored cross sign on those import lines), but while trying to run the app, I am getting an error as shown in the figure. Can anyone give me a step by step help on what to do now? I am new to GWT.

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